Fertilizer granulate containing magnesium, sulphate and urea

ABSTRACT

Disclosed is a spherical fertiliser granulate, which contains magnesium, sulphate and urea, each with respect to the total weight of the granulate, in the following quantities: Urea, calculated as elemental nitrogen, in a quantity of 20.0 to 38.0 wt %, magnesium, calculated as elemental magnesium, in a quantity of 1.5 to 9.5 wt % and sulphate, calculated as elemental sulphur, in a quantity of 2.7 to 12.0 wt %, wherein at least a portion of the magnesium, the urea and the sulphate is present in the form of at least one of the crystalline phases of the formulae MgSO4*6 NH2—C(═O)—NH2*0.5 H2O (I) and MgSO4*4 NH2—C(═O)—NH2*H2O (II), wherein 1 to 20 wt %, in particular 3 to 18 wt % and especially 5 to 15 wt % of the magnesium contained in the fertilizer granulate, calculated in each case as elemental magnesium, is present in the form of water-insoluble magnesium salts. Disclosed also is a process for manufacturing the fertiliser granulate as well as the use of the fertiliser granulate as fertiliser or in fertiliser mixtures.

The present invention relates to fertilizer granulate containingmagnesium, sulphate and urea, a process for their preparation and theuse of the fertilizer granulate as fertilizers or in fertilizermixtures.

Although at about 1.94% magnesium is the eighth most abundant element inthe earth's crust, soils often lack magnesium. Therefore, magnesiumsalts are widely used as fertilizers or fertilizer additives. Inparticular, magnesium sulphate, often in the form of monohydrate,5/4-hydrate or heptahydrate (Epsom salt), is used as a fertilizer orfertilizer additive. In this case, magnesium sulphate is typically usedin the form of magnesium sulphate-containing granulate, optionallycontaining other macronutrients such as potassium, phosphorus ornitrogen and optionally micronutrients such as manganese, zinc, copper,iron, molybdenum or boron.

Often one would like to use magnesium sulphate together with urea asfertilizer. Thus, B. von Rheinbaben, Fertilizer Research 11 (1987)describes that the combined use of magnesium sulphate monohydrate andurea leads to a reduction in nitrogen loss. However, there are limits tothe combined use of magnesium and urea. For instance, solid mixtures ofmagnesium sulphate granulate and urea are not stable in storage. Oftenafter already a short time, a reaction occurs between the twoconstituents of the mixture and the ambient humidity, leading to theformation of pasty masses which also easily deliquesce and are,therefore, difficult to handle. These can no longer be used asfertilizers in solid form. Even when stored in dry conditions, caking ofthe mixture is observed after some time. These problems occur especiallywith granulate with a high urea content.

GB 1359884 proposes to use aqueous concentrates obtained by mixing ahydration water or crystallization water containing magnesium sulphate,e.g. Epsom salt (magnesium sulphate heptahydrate), with solid urea.However, liquid fertilizer compositions are less suitable for someapplications than solid fertilizer compositions.

DE 1183058 describes the use of calcined kieserite for preparinggranules. It is suggested to combine calcined kieserite with urea in a1:1 weight ratio. The process does not result in stable granules.Moreover, the process for its production requires the preparation ofkieserite which is time and energy consuming.

DE 3320181 describes fertilizer granules containing magnesium, sulphurand nitrogen in the form of the double salt magnesium ammonium sulphateof the formula MgSO₄ (NH₄)₂SO₄.x H₂O, where x is the amount of water andmay be 0.

WO 2013/098367 proposes to solve the problem of providing a solidfertilizer composition of magnesium, sulphur and nitrogen by usingmagnesium sulphate and urea in the form of a complex compound [MgSO₄.mCO(NH₂)₂.n H₂O], wherein m is in the range of 0.9 to 1.1 and n is in therange of 2.9 to 3.1, wherein the compositions described therein beingallowed to contain little or no free MgSO₄ and less than 10 wt %unbound/unreacted urea. Preparation is carried out by reaction ofcalcined magnesium sulphate (CMS) with urea.

A similar approach is pursued by WO 2014/096372, which describescompositions consisting essentially of a magnesium sulphate-urea complexcompound of the formula [MgSO₄.m CO(NH₂)₂.p H₂O], wherein m is in therange of 0.9 to 1.1 and p is in the range of 1.9 to 2.1, or a mixturethereof with the corresponding trihydrate (p=2.9-3.1).

The disadvantage is that the complex compounds must be preparedbeforehand, and the reaction masses must be crushed. Spherical granulatecannot be produced this way. In addition, these compositions have only alow nitrogen content. It is also disadvantageous that CMS is needed forthe production as a raw material, which has to be prepared bydehydration of kieserite at 450° C., which is energy-intensive. Inaddition, such products have a high proportion of fine particulatematerial, which is disadvantageous for a number of applications.

DD 270899 describes an N—Mg fertilizer granulate with a N:Mg ratio inthe range of 2.6:1 to 8.6:1. For the preparation prilled urea issuccessively powdered with a fine particulate powder of magnesiumsulphate heptahydrate, followed by a powder of anhydrous magnesiumsulphate and finally a powdering agent such as bentonite. The process iscomplicated, and the products produced have a high dust content.

K. Honer, et al., ACS Sustainable Chem. Eng. 2017, 5(10), pp. 8546-7550describe the preparation of calcium and magnesium sulphate ureacompounds by milling urea with a calcium or magnesium sulphate hydrate.Among other things, the compound [MgSO₄.6 CO(NH₂)₂.0.5 H₂O] isdescribed. In this case, the compositions are produced as powders onlaboratory scale. The production of granulate is not possible in thisway.

CN 110041114 describes a fertilizer granulate containing 35 to 65 wt %of magnesium sulphate and 28 to 65 wt % of urea and having a nitrogencontent of 12 to 31 wt % and a magnesium content, calculated as MgO, inthe range of 9 to 20 wt %. The granulate is obtained by mixing crushedurea and magnesiumsulfate with water in a high speed mixer whilemaintaining a temperature of 50 to 85° C. for 3 to 20 minutes to achievefull contact of the components, extruding the mixture followed byripening. Thereby, the components react to form the complex compound ofthe formula [MgSO₄.CO(NH₂)₂.m H₂O]. Unfortunately, the mechanicalstability of the granulate is not satisfactory.

The invention is therefore based on the problem to provide appropriategranulate as fertilizers consisting essentially of magnesium in the formof a sulphate and urea, which do not, or only to a lesser extent, havethe above-mentioned disadvantages of the magnesium-sulphate-nitrogencompositions according to prior art. In particular, the granulate shouldnot deliquesce upon contact with atmospheric moisture and should havegood mechanical properties, for example low abrasion and/or goodhardness. These properties should also be ensured even for a high ureacontent of at least 20 wt %, calculated as nitrogen and with respect tothe total weight of the granulate, or at mass ratios of nitrogen tosulphur of at least 1.8:1, in particular at least 2.0:1 and especiallyat least 2.2:1. Moreover, it is desirable to provide uniformly shapedgranules, especially with a narrow grain spectrum, so that a more evenapplication is possible. In addition, the granulate should be producedin a simple manner and also be amenable to large-scale production. Inparticular, the granulate should be prepared from raw materials that areeasily and available and low priced. Furthermore, the granulate shouldhave a reduced tendency towards NH₃ emissions.

Surprisingly, it has been found that a fertilizer granulate based onmagnesium, sulphate and urea, which, with respect in each case to thetotal weight of the granulate, with a urea content of 20.0 to 38.0 wt %,calculated as elemental nitrogen, a magnesium content of 1.5 to 9.5 wt%, in particular 1.5 to 8.8 wt %, calculated as elemental magnesium, anda sulphate content, calculated as elemental sulphur, of 2.7 to 12.0 wt%, in particular 2.7 to 11.0 wt %, has advantageous mechanicalproperties, if at least a portion of the magnesium, the urea and thesulphate is present in the form of the crystalline phase of formula (I)and/or formula (II):

MgSO₄.6 NH₂—C(═O)—NH₂.0.5 H₂O   (I)

MgSO₄.4 NH₂—C(═O)—NH₂.H₂O   (II),

and wherein 1 to 20 wt %, in particular 3 to 18 wt % and especially 5 to15 wt % of the magnesium contained in the fertilizer granulate,calculated in each case as elemental magnesium, is present in the formof water-insoluble magnesium salts.

Accordingly, the present invention relates to a fertilizer granulatecontaining magnesium, sulphate and urea, with respect in each case tothe total weight of the granulate, in the following quantities:

-   Urea, in an amount of 20.0 to 38.0 wt %, in particular 21.0 to 36.0    wt % and especially 22.0 to 34.0 wt %, calculated as elemental    nitrogen;-   magnesium in an amount of 1.5 to 9.5 wt %, in particular 1.5 to 8.8    wt %, more particularly 2.5 to 8.7 wt % and especially 3.0 to 8.6 wt    %, calculated as elemental magnesium; and-   sulphate in an amount of 2.7 to 12.0 wt %, in particular 2.7 to 11.0    wt %, more particularly 2.8 to 10.8 wt % and especially 3.0 to 10.6    wt %, calculated as elemental sulphur,    wherein 1 to 20 wt %, in particular 3 to 18 wt % and especially 5 to    15 wt % of the magnesium contained in the fertilizer granulate,    calculated in each case as elemental magnesium, is present in the    form of water-insoluble magnesium salts.

According to the invention, at least a portion of the magnesium, theurea and the sulphate is present in the granulate in the form of atleast one of the crystalline phases of formula (I) and/or formula (II).

The invention also relates to a process for preparing the fertilizergranulate according to the invention. The process comprises providing asalt mixture containing magnesium sulphate hydrate, a water insolublemagnesium salt and particulate urea, wherein the weight ratio of thetotal weight of magnesium salts to urea is in the range of 1.2:1 to 1:5,in particular in the range of 1.1:1 to 1:4, especially in the range of1:1 to 1:3 and wherein 1 to 20 wt %, in particular 3 to 18 wt % andespecially 5 to 15 wt % of the magnesium, with respect to the totalquantity of the magnesium contained in the salt mixture and calculatedin each case as elemental magnesium, is present in the form ofwater-insoluble magnesium salts, and subjecting the salt mixture to agranulation process in the presence of added water.

The invention has a number of advantages. For instance, even at highurea contents and thus at nitrogen contents of at least 20 wt %, inparticular at least 21% by weight and especially at least 22% by weight,calculated as nitrogen and with respect to the total weight of thegranulate, or at mass ratios of nitrogen to sulphur of at least 1.8:1,in particular at least 2.0:1 and especially at least 2.3:1, thegranulate also possesses good mechanical properties, for example lowabrasion and/or a good hardness. In addition, unlike mixtures of ureaand known magnesium sulphate fertilizers, they also show no significanttendency to deliquesce or to cake even at such nitrogen levels.Furthermore, the granulate can be produced in a simple manner and isalso amenable for large-scale production. In addition, the granulateaccording to the invention can be prepared from readily available rawmaterials such as urea, synthetic magnesium sulphate (SMS) or naturalmagnesium sulphate hydrates such as magnesium sulphate monohydrate(Kieserite) or magnesium sulphate dihydrate. The granulate according tothe invention also shows a reduced tendency towards NH₃ emission afterfertilization. Correspondingly, the granulate according to the inventionis particularly appropriate as fertilizer or as a component infertilizer compositions.

Accordingly, the invention also relates to the use of the granulateaccording to the invention as fertilizer or in fertilizer compositions.The invention also relates to a method for fertilizing soils, comprisingapplying a fertilizer granules according to the invention or afertilizer composition containing a fertilizer granulate according tothe invention to the soil being fertilized.

Here and in the following, the given amount of nitrogen refers to theamount of nitrogen calculated as elemental nitrogen, if not statedotherwise. Here and in the following, the given amount of magnesiumrefers to the amount of magnesium calculated as elemental magnesium, ifnot stated otherwise. Here and in the following, the given amount ofsulphate refers to the amount of sulphate calculated as elementalsulfur, if not stated otherwise. Any values which refer to the totalweight or total mass of the fertilizer granulate relate to the dry massof the fertilizer granulate, i.e. to the mass of the fertilizergranulate containing not more than 1.5% by weight of unbound water, i.e.water which is not hydrate water. Any unbound water can be determinedvia Karl Fisher titration.

In the granulate of the invention the grains or granules, respectively,may have a spherical shape or they may be irregularily formed. Here andin the following, spherical means that the granulate grains have aregular shape which corresponds approximately to a sphere, wherein themaximum extent of the grain in a spatial direction usually does notdiffer by more than 30% of the volume equivalent diameter of therespective grain. The volume equivalent diameter is defined as thediameter of a geometric sphere with the same volume as the volume of thegrain.

Here and in the following, the terms granules and grains are usedsynonymously and refer to the particles of the granulate.

The formulas CO(NH₂)₂ and NH₂—C(═O)—NH₂ are used here and in thefollowing synonymously and stand for urea.

As already mentioned, the fertilizer granulate according to theinvention comprises urea, magnesium and sulphate, wherein at least aportion of the magnesium, the urea and the sulphate is present in theform of the crystalline phase of formula (I) and/or formula (II).

The granulate according to the invention contains at least one of thecrystalline phases of formulae (I) and (II). In the granulate of theinvention, only one of the crystalline phases of the formulae (I) or(II) or both crystalline phases of the formulae (I) and (II) may bepresent. The crystalline phases of formulae (I) and (II) can be detectedby X-ray powder diffractometry using a crushed or milled sample of thegranules based on their characteristic reflections.

The crystalline phase of formula (I) in an X-ray powder diffractogramrecorded at 25° C. (Cu-K_(α)-radiation: λ=1.5413 Å) has at least 3 andin particular at least 5 and especially at least 7 or all reflections atthe d-values (lattice plane spacings) indicated in the followingTable 1. Preferably, such an X-ray powder diffractogram has at least 3,in particular at least 5 and especially at least 7 of those reflections,whose relative intensity is larger than 8%, with respect to theintensity of the strongest peak (100% rel. intensity). In Table 1, thecharacteristic reflections of the crystalline phase of formula (I) aregiven as lattice spacings d (in Ångstroms), which can be calculated fromBragg's 2θ-values.

TABLE 1 d-values of the phase of formula (I) d-value (Å)* Rel. intensity(%) 6.057 100 5.845 54 3.775 44 5.262 33 4.000 29 3.639 22 4.114 203.029 19 4.083 12 3.108 12 2.871 11 *The first three d-values shown inTable 1 are typically always observed in a sample containing the phase.The relative intensities are to be understood as orientation only andrefer to the most intense peak (100% peak).

The crystalline phase of formula (II) in an X-ray powder diffractogramrecorded at 25° C. (Cu-K_(α)-radiation: λ=1.5413 Å) has at least 3 andin particular at least 5 and especially at least 7 or all reflections atthe d-values (lattice plane spacings) indicated in the followingTable 1. Preferably, such an X-ray powder diffractogram has at least 3,in particular at least 5 and especially at least 7 of those reflections,whose relative intensity is larger than 8%, with respect to theintensity of the strongest peak (100% rel. intensity). In Table 2, thecharacteristic reflections of the crystalline phase of formula (II) aregiven as lattice spacings d (in Ångstroms), which can be calculated fromBragg's 2θ-values.

TABLE 2 d-values of the phase of formula (II) d-value (Å)* Rel.intensity (%) 6.145 100 4.010 91 3.938 76 7.876 62 6.589 57 5.064 553.540 52 4.460 42 3.323 39 2.944 37 *The first three d-values shown inTable 2 are typically always observed in a sample containing the phase.The relative intensities are to be understood as orientation only andrefer to the most intense peak (100% peak).

The total content of the crystalline phases selected from the phases offormulae (I) and (II) in the fertilizer granulate according to theinvention is frequently at least 10 wt %, in particular at least 20 wt%, with respect to the total mass of the fertilizer granulate and can beup to 100 wt % of the fertilizer granulate. In particular, the totalcontent of the crystalline phases of formulae (I) and (II) in thefertilizer granulate according to the invention is in the range of 10 to90 wt %, in particular in the range of 20 to 80 wt %, with respect tothe total mass of the fertilizer granulate. Accordingly, 10 to 100 wt %,often 10 to 90 wt %, in particular at least 20 to 80 wt % of themagnesium contained in the fertilizer granules in the form of thecrystalline phases of formulae (I) and/or (II) is usually present.Accordingly, 10 to 100 wt %, often 10 to 90 wt %, in particular at least20 to 80 wt % of the sulphate contained in the fertilizer granulate inthe form of the crystalline phases of formulae (I) and/or (II) isusually present.

In the fertilizer granulate according to the invention, a part of themagnesium may not be present in any of the phases of formulae (I) or(II), not least due to production reasons. The magnesium not present inany of the phases of formulae (I) or (II) may be in the form of amagnesium sulphate hydrate, such as in the form of the monohydrate, i.e.in the form of Kieserite, or as 5/4 hydrate, or as a mixture ofmagnesium sulphate and one or more further salts of magnesium such asmagnesium chloride or magnesium oxide. The magnesium in the granulate ofthe invention, which is not present in any of the phases of formulae (I)or (II), may also be in the form of a crystalline magnesium sulphateurea phase, which is different from the formulae (I) and (II), e.g. inthe form of the crystalline phases of the formulae (III) and/or (IV):

MgSO₄.NH₂—C(═O)—NH₂.2H₂O   (III);

MgSO₄.NH₂—C(═O)—NH₂3H₂O   (IV).

The crystalline phases of formulae (III) and (IV) can be detected byX-ray powder diffractometry using a crushed or milled sample of thegranules based on their characteristic reflections. In Table 3, thecharacteristic reflections of the crystalline phases of formulae (III)and (IV) are given as lattice spacings d (in Ångstroms), which can becalculated from Bragg's 2θ-values.

The fertilizer granulate according to the invention may also contain aportion of magnesium, which is not in the form of the phases of formulae(I) or (II), not least due to production reasons. Usually, the portionof magnesium, which is not present in any of the phases of formulae (I)or (II), is at least 10 wt %, in particular at least 20 wt %, butusually not more than 90 wt %, in particular not more than 80 wt %, moreparticularly 10 to 90 wt %, especially 20 to 80 wt %, with respect tothe total amount of magnesium contained in the fertilizer granulate.

The fertilizer granulate according to the invention may contain aportion of magnesium in the form of a crystalline phase of the formulae(III) and/or of the formula (IV). Regarding the mechanical stability ofthe granulate, it is preferred, if the total amount of magnesium, whichis in the form of the phases of formulae (III) and/or (IV), is not morethan 20 wt %, in particular not more than 10 wt %, especially not morethan 5 wt %, e.g. in the range from 1 to 5 wt %, with respect to thetotal amount of magnesium contained in the fertilizer granulate. Thetotal amount of the crystalline phases of formulae (III) and/or (IV), ispreferably not more than 10 wt %, in particular not more than 5 wt %,with respect to the total weight of the granulate. In particular, thecrystalline phases of formulae (III) and/or (IV) are below detectionlimit.

In particular, a portion of the magnesium is present, usually at least10 wt %, in particular at least 20 wt %, but usually not more than 90 wt%, especially 20 to 90 wt %, with respect to the total amount ofmagnesium contained in the fertilizer granules, in the form of magnesiumsulphate monohydrate or magnesium sulphate 5/4-hydrate or as a mixtureof magnesium sulphate monohydrate with magnesium sulphate 5/4-hydrate.Also small amounts of magnesium sulphate dihydrate may be present.

In a particular group 1 of embodiments, the fertilizer granulatesaccording to the invention contain the crystalline phase of formula (I).In this group of embodiments, the content of the crystalline phase offormula (I) in the fertilizer granulate is typically in the range of 10to 89 wt %, in particular in the range from 20 to 77 wt % or 20 to 65 wt%, with respect to the total mass of the fertilizer granulate.Accordingly, 10 to 100 wt %, often 10 to 89 wt %, in particular 15 to 77wt % or 20 to 65 wt % of the magnesium contained in the fertilizergranules is usually present in the form of the crystalline phase offormula (I). Accordingly, 10 to 100 wt %, often 10 to 89 wt %, inparticular 15 to 77 wt % or 20 to 65 wt % of the sulphur contained inthe fertilizer granules is usually present in the form of thecrystalline phase of formula (I). In this particular group 1 ofembodiments, the amount of the crystalline phase of formula (II) istypically lower than the amount of the crystalline phase of the formula(I). Typically, the mass ratio of the crystalline phase of formula (II)to the crystalline phase of formula (I) is not more than 1:1.5, inparticular not more than 1:2 or may be even 0, i.e. the amount ofcrystalline phase of formula (II) is below its limit of detection. Inthis group 1 of embodiments, the amount of the crystalline phase offormula (II) typically does not exceed 15 wt %, with respect to thetotal mass of the fertilizer granulate. The fertilizer granulate ofgroup 1 of embodiments may additionally contain at least one of thecrystalline phases of the formula (III) and/or of the formula (IV).Regarding the mechanical stability of the granulate, it is preferred, ifthe total amount of magnesium, which is in the form of the phases offormulae (III) and/or (IV), is not more than 15 wt %, in particular notmore than 10 wt %, with respect to the total amount of magnesiumcontained in the fertilizer granulate. The total amount of thecrystalline phases of formulae (III) and/or (IV), is preferably not morethan 10 wt %, in particular not more than 5 wt %, with respect to thetotal weight of the granulate. In particular, the crystalline phases offormulae (III) and/or (IV) are below detection limit.

In another particular group 2 of embodiments, the fertilizer granulatesaccording to the invention contain the crystalline phase of formula(II). In this group of embodiments, the content of the crystalline phaseof formula (II) in the fertilizer granulate is typically in the range of10 to 89 wt %, in particular in the range from 20 to 77 wt % or 20 to 65wt %, with respect to the total mass of the fertilizer granulate.Accordingly, 10 to 100 wt %, often 10 to 98 wt %, in particular at least15 to 77 wt % or 20 to 65 wt % of the magnesium contained in thefertilizer granules is usually present in the form of the crystallinephase of formula (II). Accordingly, 10 to 100 wt %, often 10 to 89 wt %,in particular at least 15 to 77 wt % or 20 to 65 wt % of the sulphatecontained in the fertilizer granulate is usually present in the form ofthe crystalline phase of formula (II). In this particular group 2 ofembodiments, the amount of the crystalline phase of formula (I) istypically lower than the amount of the crystalline phase of the formula(II). Typically, the mass ratio of the crystalline phase of formula (I)to the crystalline phase of formula (II) is not more than 1:1.5, inparticular not more than 1:2 or may be even 0, i.e. the amount ofcrystalline phase of formula (I) is below its limit of detection. Inthis group 2 of embodiments, the amount of the crystalline phase offormula (I) typically does not exceed 20 wt %, with respect to the totalmass of the fertilizer granulate. The fertilizer granulate of group 2 ofembodiments may additionally contain at least one of the crystallinephases of the formula (III) and/or of the formula (IV). Regarding themechanical stability of the granulate, it is preferred, if the totalamount of magnesium, which is in the form of the phases of formulae(III) and/or (IV), is not more than 15 wt %, in particular not more than10 wt %, with respect to the total amount of magnesium contained in thefertilizer granulate. The total amount of the crystalline phases offormulae (III) and/or (IV), is preferably not more than 10 wt %, inparticular not more than 5 wt %, with respect to the total weight of thegranulate. In particular, the crystalline phases of formulae (III)and/or (IV) are below detection limit.

The fertilizer granulate according to the invention contains a smallportion of magnesium as water-insoluble magnesium salts. The amount ofmagnesium in the form of water-insoluble magnesium salts is in the rangefrom 1 to 20 wt %, in particular 3 to 18 wt % and especially 5 to 15 wt%, with respect to the total amount of magnesium contained in thegranulate. The water-insoluble magnesium salts are magnesium saltshaving a solubility in deionized water at 22° C. of not more than 500mg/L. They are in particular inorganic magnesium salts including, forexample, magnesium oxide, magnesium carbonate, magnesium hydroxide,magnesium silikates, magnesium aluminates, magnesium alumosilicates andmixtures thereof. The total amount of magnesium in the form ofwater-insoluble magnesium salts in the granulate is typically in therange of 0.2 to 2 wt %, in particular 0.3 to 1.5%, based on the totalweight of the granulate and calculated as elemental magnesium. Thepresence of magnesium in the form of water-in-soluble magnesium saltsimproves the mechanical properties of the granulate and results in anincreased burst strength and reduced abrasion. The amount ofwater-insoluble magnesium sulfate can be determined indirectly by firstdetermining the total magnesium content. For this, a first portion ofthe crushed granule is completely dissolved in deionized watercontaining 1 wt % of nitric acid, and the amount of magnesium in theaqueous solution is determined by elemental analysis. Then, a secondportion of the crushed granulate is dissolved in deionized water of pH 7at 22° C. for 24 h with stirring. The insoluble matter is removed byfiltration, and the amount of magnesium in the aqueous solution isdetermined by elemental analysis. Thus, the amount of soluble magnesiumis determined. The difference between the total amount of magnesium andthe amount of soluble magnesium is the amount of insoluble magnesium.Comparison with the total amount of magnesium contained in the granulategives the relative amount of magnesium, which is present as waterinsoluble magnesium salts.

The fertilizer granules according to the invention can also contain aportion of the urea, which is not present in the form of the crystallinephases of formulae (I) and (II). The urea not present in any of thephases of formulae (I) or (II) is typically present in free/unboundform, i.e. in unreacted/non-reacted form. As pointed out above, acertain amount of urea can also be present in form of other crystallinemagnesium sulphate-urea phases, which are different to formulae (I) and(II), e.g. in the form of the crystal-line phases of the formulae (III)and/or (IV). Preferably, at least 10 wt %, in particular at least 20 wt%, especially at least 30 wt %, e.g. 10 to 100 wt %, in particular 20 to90 wt % and especially 30 to 85 wt % of the urea contained in thefertilizer granulate is present in the form of the crystalline phases offormulae (I) and/or (II). The proportion of unbound/unreacted urea willusually not exceed 90 wt %, in particular 80 wt % and especially 70 wt %of the urea contained in the granulate and is, if present, in the rangeof 10 to 80 wt %, in particular 15 to 70 wt %, with respect to the totalamount of urea contained in the granulate. The unbound/unreacted ureacan be present in the granulate in a homogeneously distributed form.

Preferably, the granulate has a conglomerate structure. In thisconglomerate structure, part of the urea contained in the granulateparticles is present in the form of crystalline urea particles embeddedin a matrix containing sulphate salts of magnesium and at least one ofthe crystalline phases of formulae (I) and (II) and optionally one orboth of the crystalline phases of the formulae (III) and/or (IV). Theseurea particles typically have diameters in the range of 0.01 to 0.5 mm.In the matrix, the sulphate salts of magnesium are preferably magnesiumsulphate hydrates such as magnesium sulphate monohydrate, magnesiumsulphate 5/4-hydrate or a mixture of magnesium sulphate monohydrate withmagnesium sulphate 5/4-hydrate. The water-insoluble salts of magnesiumare likewise embedded in the matrix as small particles.

In the fertilizer granulate according to the invention, part of thesulphate may not be present in the form of any of the phases of formulae(I) or (II), not least due to production reasons. The sulphate notpresent in any of the phases of formulae (I) or (II) is typically in theform of a magnesium sulphate hydrate, in particular in the form ofmonohydrate and/or 5/4-hydrate and/or in the form of a crystalline phaseof the formulae (III) or (IV).

Generally at least 10 wt %, in particular at least 20 wt %, butgenerally not more than 90 wt %, especially 20 to 90 wt %, with respectto the total amount of sulphate contained in the fertilizer granulate,is not present in the form of any of the phases of formulae (I) or (II).In particular, a portion of the sulphate is present, usually at least 10wt %, in particular at least 20 wt %, but usually not more than 90 wt %,especially 20 to 90 wt %, with respect to the total amount of sulphatecontained in the fertilizer granulate, in the form of magnesium sulphatemonohydrate, as a mixture of magnesium sulphate monohydrate withmagnesium sulphate 5/4-hydrate and/or in the form of a crystalline phaseof the formulae (III) or (IV).

For the properties of the fertilizer granulate, it has provenadvantageous if it contains sulphate and urea in such a ratio that themass ratio of nitrogen to sulphur is in the range of 10.5: 1 to 1.8:1,in particular in the range of 6.5:1 to 2:1, especially in the range of5:1 to 2.3:1.

The constituents contained in the fertilizer granules according to theinvention can be determined by standard analytical methods, for examplewith elemental analysis, e.g. by wet analysis or by atomic emissionspectroscopy (e.g. by ICP-OES). Crystalline constituents other than thephases of formulae (I) or (II) can also be detected by X-ray powderdiffractometry. For example, constituents such as unreacted urea andmagnesium sulphate monohydrate can be identified in an X-ray powderdiffractogram of the composition, recorded at 25° C. (Cu-K_(α)radiation: λ=1.5413 Å), by means of the reflections given in thefollowing Table 3, whereby for identification typically at least 3 ofthe indicated d-values with a relative intensity greater than 10% areused.

TABLE 3 d-values of the other constituents of the fertilizer granulateOther Constituents d-value (Å) Rel. intensity (%) Urea 4.010 100 3.62025 3.040 30 2.528 12 2.422 10 MgSO₄•H₂O 3.405 100 4.815 75 3.351 703.313 70 MgSO₄•5/4 H₂O 3.370 100 3.430 60 3.230 50 4.850 40 3.170 402.570 15 MgSO₄•NH₂—C(═O)—NH₂•2 H₂O 6.937 100 (Formula III) 3.349 453.157 43 3.257 28 3.364 25 3.469 23 4.940 19 4.917 17 2.605 12 3.287 112.621 8 MgSO₄•NH₂—C(═O)—NH₂•3 H₂O 10.1656 100 (Formula IV) 3.3994 633.8527 39 4.0752 21 2.9318 15 2.7558 15 4.2520 13 3.0064 13 4.8050 93.2015 9 *Of the d-values given in Table 3, typically the first threevalues are always observed in a sample containing the respective phase.The relative intensities are to be understood as orientation only andrefer to the most intense peak (100% peak).

The relative proportions of the respective crystalline constituents canbe estimated by means of X-ray powder diffractometry on the basis ofreference diagrams.

According to the invention, the fertilizer granulate contains magnesium,sulphate and urea and optionally water, the total amount of magnesium,sulphate and urea generally 1 0 being at least 80 wt %, e.g. 80 to 100wt %, in particular 90 to 100 wt %, and especially 95 to 100 wt %, withrespect to the total mass of the fertilizer granulate, minus any watercontained therein.

Usually, the fertilizer granulate in addition to magnesium, sulphate andurea also contains water, wherein at least a part of the water ispresent in the form of crystallization water bound in the fertilizergranulate, for example as crystallization water in the phases offormulae (I) and/or (II), if present as crystallization water in thephases of formulae (III) and/or (IV) and as crystallization water inmagnesium sulphate. The fertilizer granulate may also contain unboundwater. The content of unbound water, i.e water not bound ascrystallization water, of the fertilizer granulate can be determined ina manner known per se, e.g. by Karl Fischer titration. Preferably, theunbound water does not exceed 2 wt % and is typically in the range of0.1 to 2.0 wt %, with respect to the total mass of the fertilizergranulate. Fertilizer granulates of the invention, which do not containmore 1.5 wt %, in particular not more than 1.0 wt % of unbound water areparticularly preferred with respect to their storage stability. Theunbound water can be determined by Karl Fisher titration.

Furthermore, the fertilizer granulate according to the invention mayalso contain micro-nutrients, which are also referred to as traceelements. In addition to boron, these include the elements manganese,zinc, copper, iron and molybdenum. Trace elements may also be selenium,cobalt and iodine. Boron is present preferably as sodium calcium borate,e.g. in the form of ulexite, sodium borate, e.g in the form of boraxpentahydrate, potassium borate or boric acid. The elements manganese,zinc, copper, cobalt, iron and molybdenum are typically present in thegranulate in the form of their salts or complex compounds. Manganese,copper and zinc are present preferably in the form of their sulphates.Copper and iron may also be present in the form of chelates, e.g. withEDTA. Molybdenum is present preferably as sodium or ammonium molybdateor as a mixture thereof. Typically, the proportion of micronutrientsother than boron, calculated in their elemental form, will not exceed 3wt %, with respect to the total mass of the constituents of themagnesium sulphate granulate used according to the invention. Thecontent of boron, calculated as B₂O₃, will generally not exceed 10 wt %,in particular 5 wt %, and is typically, if present, in the range from0.01 to 10 wt %, in particular 0.1 to 5 wt %, with respect to the totalmass of the components of the fertilizer granulate according to theinvention. The total amount of micronutrients or trace elements is, ifdesired, in the range of 0.01 to 10 wt %, in particular in the range of0.1 to 5.0 wt %, with respect to the total mass of the fertilizergranulate and calculated as elements.

Furthermore, the fertilizer granulate according to the invention mayalso contain biostimulants (e.g. algae and plant extracts, productsbased on mineral and/or microbial base).

The fertilizer granulate according to the invention preferably has asmall proportion of granules with a particle size or grain size of lessthan 1 mm. In particular, the proportion of granules with a particlesize below 1 mm is less than 10 wt %, in particular less than 5 wt %.Frequently, at least 80 wt % and especially at least 90 wt % of thegranules have a particle size of not more than 10 mm. The particle sizedistribution of the granules is preferably such that at least 70 wt %,in particular at least 80 wt % and especially at least 90 wt % have aparticle size in the range from 1 to 10 mm, in particular in the rangefrom 2 to 8 mm. However, the fertilizer granulate can also be present inthe form of a so-called microgranulate. In such microgranulates, usuallyat least 80 wt % and especially at least 90 wt % of the granules have agrain size of a maximum of 3 mm, in particular a maximum of 2.5 mm.Preferably, the grain size of the granules in micro-granulates is atleast 70 wt %, in particular at least 80 wt % and especially at least 90wt % in the range from 0.5 to 3 mm.

The particle size may depend on the production process. For example, agranulate obtained from an agglomeration process usually has a particlesize distribution, wherein at least 70 wt %, in particular at least 80wt % and especially at least 90 wt % have a particle size in the rangeof 1.0 to 6.0 mm, in particular in the range of 2.0 to 5.0 mm, agranulate obtained from an compaction process usually has a particlesize distribution, wherein at least 70 wt %, in particular at least 80wt % and especially at least 90 wt % have a particle size in the rangeof 2.5 to 10.0 mm, in particular in the range of 3.0 to 8.0 mm.

The particle sizes given here and below, which are also referred to asgrain sizes, are generally those values, as determined by sievinganalysis according to DIN 66165:2016-08. The determination of the massfractions of the respective particle sizes or particle size ranges takesplace in accordance with DIN 66165:2016-08 by fractionating thedispersed granulate using several sieves by means of mechanical sievingin pre-calibrated systems. Unless otherwise indicated, percentages inconnection with particle or grain sizes are to be understood asstatements in wt %. In this context, the d₉₀-value denotes that grainsize that 90 wt % of the granules fall below. The d₁₀-value denotes thatgrain size that 10 wt % of the granules fall below. The grain sizedistribution of the fertilizer granulate according to the invention isaccordingly characterized by a d₁₀-value of at least 1.5 mm and inparticular of at least 2 mm and a d₉₀-value of not more than 10 mm.

The fertilizer granulate according to the invention is usually producedby subjecting a salt mixture containing a magnesium sulphate hydrate, awater insoluble magnesium salt and particulate urea in a weight ratio inthe range of 1.2:1 to 1:5, in particular in the range of 1.1:1 to 1:4,especially in the range of 1:1 to 1:3 and optionally furtherconstituents contained in the granulate to a granulation process in thepresence of added water.

According to the invention, the process is carried out with the additionof water to at least partially achieve the conversion of the magnesiumsulphate hydrate and the urea into the crystalline phase of formulae (I)or (II) and thus to achieve the desired strength of the granules.

According to the invention, the granulation of the salt mixture iscarried out in the presence of water. The presence of the water causes apartial solubilization of the particles of the salt mixture, so that theurea reacts with the magnesium sulphate hydrate to form the crystallinephases of formulae (I) and/or (II) and optionally one more magnesiumsulphate urea phases, e.g. the crystalline phases of formulae (III)and/or (IV). The amount of water will typically be chosen such that nocomplete dissolution of the salt mixture is achieved.

Typically, the total amount of water added to the salt mixture is in therange of 1.5 to 8 wt %, in particular in the range of 2 to 7 wt %, withrespect to the mass of the urea used for granulation. Typically, thetotal amount of water in the salt mixture, i.e. the amount of addedwater and the hydrate water of the magnesium sulphate hydrate, is in therange from 3 to 15 wt %, in particular in the range from 4 to 13 wt %,with respect to the total mass of the salt mixture and added water.

Preferably, the main quantity of water used for the granulation is addedto the salt mixture before or at the beginning of the granulationprocess. Preferably at least 50 wt %, in particular at least 80 wt %, orthe total amount of water is added before or directly at the beginningof the granulation to the salt mixture. A subset of the water may alsobe added in the course of the granulation process.

Here, the magnesium sulphate hydrate in particularly is selected fromsynthetic magnesium sulphate hydrate (SMS), which already containswater-insoluble magnesium salts, and natural magnesium sulphatehydrates, which typically do not contain water-insoluble magnesiumsalts, such as magnesium sulphate monohydrate (Kieserite), magnesiumsulphate 5/4-hydrate, magnesium sulphate dihydrate, magnesium sulphatetrihydrate and mixtures thereof. Preference is given to natural orsynthetic magnesium sulphate monohydrate and mixtures of magnesiumsulphate monohydrate with magnesium sulphate 5/4 hydrate. Particularpreference is given to a magnesium sulphate hydrate which alreadycontains a water-insoluble magnesium salt, e.g. in the form ofwater-insoluble magnesium oxide or magnesium carbonate. In particular,the proportion of water-insoluble magnesium, with respect to the totalmass of the magnesium sulphate hydrate and calculated as MgO is in therange of 1.0 to 10 wt %, preferably in the range of 1.5 to 7.0 wt %,especially in the range of 1.7 to 6.0 wt %.

The composition of the salt mixture used in the granulation is usuallychosen so that its gross composition, apart from water, corresponds tothe overall composition of the granulate. Accordingly, the salt mixtureis typically composed of preferably at least 80% by weight, and morepreferably at least 90% by weight, e.g. from 80 to 100 wt %, inparticular 90 to 100 wt %, with respect to the total mass of the saltmixture, minus any water contained therein, of magnesium sulphatehydrate, water insoluble magnesium salt and urea.

The magnesium sulphate hydrate may, in principle, be naturally occurringmagnesium sulphate monohydrate, also termed kieserite, or asynthetically prepared magnesium sulphate hydrate having about 0.9 to1.5 mol of hydrate water per mol magnesium.

Synthetically prepared magnesium sulphate hydrate is preferably used forpreparing the fertilizer granulate of the present invention, andhereinafter it is also referred to as synthetic magnesium sulphatehydrate or SMS for short.

The water-insoluble magnesium salts are magnesium salts having asolubility in deionized water at 22° C. of not more than 500 mg/L. Theyare in particular inorganic magnesium salts including, for example,magnesium oxide, magnesium carbonate, calcium magnesium carbonate(dolomite), magnesium hydroxide, magnesium silikates, magnesiumaluminates, magnesium alumosilicates and mixtures thereof. Thewater-insoluble magnesium sulphate may be provided to the salt mixtureas a separate component, but it may also be provided as an intimatemixture with the magnesiumsulphate hydrate.

Synthetic magnesium sulphate hydrate is understood as meaning amagnesium sulphate hydrate, which is obtainable by reaction of causticmagnesium oxide or magnesium carbonate with sulphuric acid in asub-stoichiometric amount, in particular with a 50 to 90 wt % aqueoussulphuric acid. Substoichiometric amount means that the molar amount ofsulphuric acid is somewhat lower than the molar amount of magnesium inthe caustic magnesium oxide or magnesium carbonate and typically in therange of 0.80 mol to 99 mol, in particular 0.82 mol to 0.97 mol andespecially 0.85 mol to 0.95 mol with respect to 1 mol of magnesium inthe caustic magnesium oxide or magnesium carbonate, respectively.Caustic magnesium oxide is magnesium oxide obtained by calcination ofmagnesium carbonate.

SMS, in comparison to magnesium sulphate monohydrate from naturalsources such as kieserite, usually contains lower amounts of halides anda water-insoluble magnesium in the form of water-insoluble magnesiumsalts, in particular salts selected from magnesium oxide, magnesiumcarbonate, calcium magnesium carbonate and magnesium hydroxide, mixturesthereof as well as mixtures thereof with magnesium silicates and/ormagnesium aluminates or magnesium alumosilicates. In particular, theproportion of water-insoluble magnesium salts, with respect to the totalmass of the SMS is in the range of 0.5 to 7.0 wt %, frequently 1 to 6 wt%, especially in the range of 1.5 to 5.0 wt %, calculated as MgO, or inthe range of 0.3 to 4.2 wt %, frequently in the range of 0.6 to 3.6 wt%, especially in the range of 0.9 to 3.0 wt %, calculated as elementalMg. The proportion of magnesium in the form of water-insoluble magnesiumsalts is in the range of 1 to 20 wt %, in particular 3 to 18 wt % andespecially 5 to 15 wt %, with respect to the total amount of magnesiumcontained in the SMS. Any relative weight given herein refers to the dryweight, i.e. the weight of the SMS after drying for 2 h and 1 bar at105° C. The proportion of salts in the SMS, which are different frommagnesium sulphate and magnesium oxide, is usually less than 3 wt %, inparticular less than 2.5 wt %, with respect to the total mass of SMS.The total content of magnesium, i.e. the total amount of water-solubleand water-insoluble magnesium in the SMS is usually at least 24 wt %, inparticular at least 26 wt %, calculated as MgO, and is often in therange of 24 to 30 wt %, in particular 26 to 29 wt %. Any relativeamounts of magnesium in SMS given here refer to a relative amount withrespect to the total amount of solids in SMS, i.e. the weight of thereaction mixture after drying at 100° C. to constant weight. Thechemical pulping of magnesium oxide with aqueous sulphuric acid is knownper se and is described, for example, in CN 101486596 or CN 101624299.The aqueous sulphuric acid used for the reaction usually has an H₂SO₄concentration in the range of 50 to 90 wt %, in particular in the rangeof 55 to 85 wt %.

In the SMS, the magnesium sulphate is present mainly as magnesiumsulphate monohydrate, as a magnesium sulphate 5/4 hydrate or as amixture of magnesium sulphate monohydrate with magnesium sulphate 5/4hydrate, although small amounts of magnesium sulphate dihydrate may beincluded in the SMS. Preferably, the proportion of magnesium sulphatemonohydrate and magnesium sulphate 5/4 hydrate in the SMS is at least 90wt %, with respect to the total mass of the SMS. Particular preferenceis given to an SMS in which at least 90 wt % of the magnesium sulphate,with respect to the total amount of magnesium sulphate plus hydrationwater, is present as magnesium sulphate monohydrate. In particular, thecontent of crystallization water in the SMS is 12.0 to 16.0 wt %, withrespect to the total mass of the SMS, and determined bythermogravimetric analysis in accordance with DIN EN ISO11358-1/2013-03.

The magnesium sulphate hydrate used for granulation has a grain sizedistribution in which typically at least 80 wt %, in particular at least90 wt %, of the salt grains of the magnesium sulphate hydrate have aparticle size of not more than 1 mm, in particular not more than 0.5 mmand especially not more than 400 pm, determined by means of laser lightdiffraction according to ISO 13320:2009-10. Preferably, at least 80 wt %of the salt grains of the magnesium sulphate hydrate have a particlesize in the range from 1 to 1000 μm, in particular in the range from 2to 500 μm and especially in the range from 10 to 400 μm, determined bymeans of laser light diffraction according to ISO 13320:2009-10. Theaverage grain size (weight average, d₅₀-value) of the magnesium sulphatehydrate used for agglomeration is typically in the range from 50 to 300μm, in particular in the range from 85 to 250 μm. The maximum d₉₀-valueof the magnesium sulphate hydrate used for the agglomeration isgenerally at most 900 μm and especially at most 400 μm.

The urea used in granulation can, in general, be used in any solid formdesired. Typically, the urea used will be in prilled form or in the formof ground prills. Such urea prills generally have a urea content of atleast 95 wt %, in particular at least 98 wt %. Frequently, the nitrogencontent is about 44 to 48 wt %. The grain size of the solid urea in sucha prill is typically in the range of 0.2 to 3 mm, i.e. at least 90 wt %of the prills have a grain size in this range. But the urea can also beground before use in agglomeration to achieve better conversion. It hasbeen proven to be advantageous if the ground urea has a grain sizedistribution, wherein typically at least 80 wt %, in particular at least90 wt % of the urea grains have a grain size of not more than 1.5 mm andespecially not more than 1.0 mm and preferably have grain sizes in therange of 1 to 1000 microns, and especially in the range of 2 to 500microns, determined by laser light diffraction according to ISO13320:2009-10.

The salt mixture used to prepare the fertilizer granulate typicallycontains magnesium sulphate hydrate, the water-insoluble magnesium saltsand urea in a total amount of at least 80 wt %, in particular at least90 wt % and especially at least 95 wt %, with respect to the total massof the salt mixture minus any water contained therein, and optionallyone or more micronutrients.

Furthermore, the salt mixture used for granulation may also containorganic binders, such as tylose, molasses, gelatin, starch,lignosulphonates or salts of polycarboxylic acids such as sodium citrateor potassium citrate, fatty acid salts such as calcium stearate orsilicates, in particular phyllosilicates such as talc. The proportion oforganic binders will typically not exceed 1 wt % and in particular isless than 0.5 wt %, in each case with respect to the total mass of theconstituents of the salt mixture other than unbound water. If syntheticmagnesium sulphate hydrate is used as the magnesium sulphatemonohydrate, an organic binder can be dispensed with. In particular, thesalt mixture used for the granulation contains no organic binders or notmore than 0.1 wt %, in particular not more than 0.05 wt %, with respectto the total mass of the constituents of the salt mixture other thanunbound water. If kieserite is used as the magnesium sulphatemonohydrate, it will be preferable to use an organic binder, inparticular starch and especially wheat starch. In particular, the saltmixture used for granulation contains 0.1 wt % to 1 wt % of organicbinder, with respect to the total mass of the constituents of the saltmixture other than unbound water.

The granulation is usually carried out at temperatures in the range of20 to 80° C. Preferably, the temperature should not exceed 80° C. Forthe quality of the product it was found beneficial that during thepreparation the granulate or the salt mixture is subjected to atemperature in the range of 50 to 80° C., in particular in the range of55 to 80° C. Preferably, such a temperature is maintained duringgranulation for at least 5 minutes, e.g. for a time period in the rangeof 5 min. to 12 h. This can be achieved, for example, if the granulationis carried out at temperatures in the range of 50 to 80° C., inparticular in the range of 55 to 80° C., and/or the fresh productobtained in the granulation process is subjected to a heat treatment inthe range of 50 to 80° C., in particular in the range of 55 to 80° C.The temperature data refer to the temperature of the salt mixture or tothe temperature of the fresh granulate product, as it can be measuredfor example by means of an infrared sensor. If the granulation processis carried out at elevated temperature, the salt mixture and/or thewater can be heated. Optionally, a higher temperature can be used at thebeginning of granulation and reduced during the granulation process,wherein also from the beginning of granulation preferably a value of 80°C. should not be exceeded in order to avoid or reduce conversion of theurea into biuret.

The actual implementation of granulation can be carried out analogouslyto the granulation processes known from the prior art, which aredescribed, for example, in Wolfgang Pietsch, Agglomeration Processes,Wiley-VCH, 1^(st) Edition, 2002, in G. Heinze, Handbuch derAgglomerationstechnik, Wiley-VCH, 2000 and in Perry's ChemicalEngineers' Handbook, 7^(th) Edition, McGraw-Hill, 1997, 20-73 to 20-80.Here and in the following the terms agglomeration and granulation areused synonymously.

According to one group A of embodiments, the granulation is carried outby an agglomeration process. In the granulation by means ofagglomeration, the particles of the salt mixture are set in motionduring the granulation process and treated with water. As mentionedabove, the water causes at the very least a partial solubilisation ofthe particles of the salt mixture, so that the urea reacts with themagnesium sulphate hydrate to form the crystalline phases of formulae(I) and/or (II) and optionally one more magnesium sulphate urea phases,e.g. the crystalline phases of formulae (III) and/or (IV). In addition,the water causes the particles of the salt mixture to agglomerate intolarger particles, since by the presence of water liquid bridges can beformed between the particles of the salt mixture, which lead to adhesionof the particles. At the same time, the forced movement of the particlesand the associated kinetic energy of larger agglomerates promotes theformation of comparatively uniformly-sized agglomerates with a sphericalgeometry. As the liquid bridges contain the dissolved components of thesalt mixture, they will form solid material upon drying of the moistgranules, thereby increasing the adherence between the particles of thesalt mixture, which form the grains and thus increasing the mechanicalstrength of the grains.

In this context, it has proven to be advantageous if the agglomerationof group A of embodiments is carried out in such a way that in thecourse of the agglomeration the reaction mixture is present temporarilyin viscid state, i.e. in viscous form, in particular at least at thebeginning of agglomeration. Furthermore, it has proved to beadvantageous if the constituents of the salt mixture are present atleast partially in dissolved form at the beginning of agglomeration.This can be achieved by the way in which the water is added, by thechoice of the amount of water and the temperature.

It has been found to be advantageous if the salt mixture is chargedinitially, and to add at least one subset, preferably at least 50 wt %,in particular at least 80 wt %, or the total amount of water directly atthe beginning of the agglomeration. A subset of the water may also beadded in the course of the agglomeration.

The agglomeration, in particular the mixed agglomeration, preferablytakes place at temperatures in the range from 55 to <80° C., inparticular in the range from 65 to <80° C. These temperature data referto the temperature of the salt mixture, as it can be measured, forexample, by means of an infrared sensor. Optionally, the reactionmixture can be heated. Optionally, a higher temperature can be used atthe beginning of agglomeration and reduced during the agglomerationprocess, wherein also from the beginning of agglomeration preferably avalue of 80° C. should be maintained or should not be exceeded.

In this context, it has proven to be advantageous for the strength ofthe granulate if at least a part, in particular at least 40 wt % of thewater contained in the reaction mixture is removed by evaporation duringthe agglomeration and/or during an optionally subsequent maturing phase,so that the granulate immediately after its preparation has an unboundwater content of not more than 5 wt %, in particular not more than 2 wt%, especially not more than 1.5 wt %, determined by Karl Fischertitration.

Agglomeration can be carried out, for example, as a roll, mixed orfluidized bed agglomeration. Also appropriate are combinations of thesemeasures, e.g. a combination of mixed and roll agglomeration or acombination of roll, mixed and fluidized bed agglomeration. Theagglomeration according to the invention preferably comprises a mixedagglomeration in an intensive mixer, especially in an Eirich mixer. Inthe case of mixed agglomeration, the particulate salt mixture previouslymoistened with at least one subset, in particular the main amount andespecially the total amount of water, is added to an intensive mixer,especially an Eirich mixer, i.e. in an intensive mixer type as sold bythe company Maschinenfabrik Gustav Eirich GmbH & Co KG. An intensivemixer typically comprises a container having an inclined axis ofrotation and a circular cross-section, which preferably features furthercomponents that promote mixing, in particular at least one mixing tool,especially at least one rotating mixing tool, and optionally one or morefixed components, e.g. scraper. By rotating the container, the particlesof the salt composition are set in motion and the granulation process isinitiated. When adding water to the salt mixture, as a rule, theformation of irregularly shaped agglomerates starts to occur, which arethen converted into more regularly shaped agglomerates/granules duringmixed agglomeration. In general, mixed agglomeration occurs at the abovementioned temperatures. In the case of mixed agglomeration, it hasproven to be advantageous to work initially at a higher temperature, butpreferably <80° C., and to reduce the temperature in the course ofagglomeration, e.g. by up to 25° C. Preferably, a partial amount of thewater used in the beginning is removed again during the mixedagglomeration, for example by means of an air stream.

According to another group B of embodiments the granulation is carriedout by a compaction process in the presence of water.

For the purposes of the invention, the term “compaction” refers to theproduction of granules comprising a step, where pressure is excerted onthe salt mixture. Compaction may be achieved simply by pressing or bybriquetting described in more detail below.

Typically, the compaction granulation comprises the steps of mixing themagnesium sulphate hydrate, the particulate urea and water, followed bysubjecting the obtained mixture to a compaction granulation to obtaingranules. Preferably, the obtained granules are subjected to asubsequent heating step.

In order to achieve an even distribution of the components of the saltmixture within the grains of the granulate, the urea and the magnesiumsulphate hydrate are mixed in a mixing device, especially in anintensive mixer. For this purpose, the finely divided raw materials,i.e. urea and the magnesium sulphate hydrate, are fed into the mixingdevice, in particular an intensive mixer. For the purpose of theinvention, the salt mixture is moistened by the addition of water.Typically, the main quantity of water used for the granulation is addedto the salt mixture during mixing. Preferably at least 50 wt %, inparticular at least 80 wt %, or the total amount of water is added tothe salt mixture during mixing to the salt mixture.

The thus obtained moistened salt mixture is then subjected to acompaction process. In the compaction process, the particles of themoistened salt mixture are typically compacted by means of a press.Thereby a compacted material consisting essentially of the components ofthe moistened salt mixture is obtained. Depending on the type ofcompaction, the fine-particle components of the mixture are agglomeratedto form coarse agglomerates or strip-like strands or flakes,respectively. Depending on the type of press agglomeration, thecoarse-particle material obtained during compacting is then eithercrushed or separated. Basically all presses known for similar purposesare suitable for compacting, such as punch presses, extrusion presses,piercing presses and roller presses.

The compaction may be carried out at the temperature given above for thegranulation. Preferably the temperature should not exceed 80° C.Typically, the compaction is carried out at a temperature in the rangefrom 20 to 70° C. While heating of the salt mixture subjected to thecompaction is not required, it may be beneficial to heat the saltmixture before or during compaction to a temperature in the range of atleast 40° C., in particular at least 50° C., especially at least 55° C.or at least 65° C., e.g. to a temperature in the range of 40 to 80° C.,in particular in the range 50 to 80° C., in particular in the range of55 to 80° C. or 65 to 80° C. The fresh product obtained in thecompaction process is preferably subjected to a heat treatment in therange of 50 to 80° C., in particular in the range of 55 to <80° C. Thisheat treatment is also termed maturation and described hereinafter.

Preferably, compacting of the moistened salt mixture is carried outusing a roller press. In roller presses, compaction takes place in thegap between two rollers rotating in opposite directions. The rollersurfaces can be smooth, profiled, e.g. corrugated, waved, or equippedwith mould troughs. Any profiling of the roll surface serves primarilyto improve the feed ratio into the roll nip.

In a preferred subgroup B1 of group B of embodiments of the invention,compacting is carried out by means of a roller press, the rollers ofwhich are equipped with mould cavities. Such rolling rolls are alsocalled shaped rolls. Typical mould cavities have hemispherical,semi-ellipsoidal, semi-cylindrical or semi-cushioned geometries. Thedimensions of the mould cavities are selected so that two mould cavitiescorrespond approximately to the desired dimensions of the granules to beproduced. Preferably, the mould cavities have a depth of about 1 to 4mm. The radius or axis length of the circular or elliptical sectionalarea of the spherical or semi-ellipsoidal mould cavities with the rollsurface is typically in the range of 2 to 10 mm, in particular 3 to 8mm. The same applies to the edge lengths of the cut surfaces of thesemi-cylindrical or semi-cushioned mould cavities with the roll surface.

In this way, a flake of preformed granules is obtained, which areconnected to each other by thin webs. The granules preformed in this wayare separated by the application of mechanical forces, e.g. by using aan impact crusher and/or a roll crusher, e.g. a spike roll crusher. Fromthe thus obtained granulate, small particles, i.e. debris or fragments,may be removed, e.g. by sieving. The coarse partkels may be smoothed atthe fracture surfaces, which is also referred to as mechanical rounding,filleting or rounding. This is typically done in a device suitable forrounding granules, for example a spheronizer or a drum screen. In thisway, a uniformly shaped granulate is obtained with dimensions and shapesdetermined by the mould cavities. Examples of such shapes are spheres,ellipsoids, rods and pillow shapes, which are also referred to asmini-briquettes in the following. As a rule, 90% of the granules thusobtained have a grain size in the range of 2 to 10 mm, in particular 3to 8 mm, determined by sieve analysis according to DIN 6165:2016-08.

During separation and rounding, dust is naturally produced in additionto the granulate, which corresponds to the chemical composition of thesalt mixture. This dust can be partially or completely recycled into theraw material or into the salt mixture.

In another preferred subgroup B2 of group B of embodiments of theinvention, compacting of the moistened salt mixture is carried out bymeans of a roller press, the rolls of which have a smooth or profiledroll surface. In this case, the primary agglomeration product is aflake-like or plate-like strand emerging from the roll nip, which isalso referred to as a flake or schülpe, respectively. The pressingforces required for compaction, which are usually related to the rollwidth and specified as linear forces, are generally in the range of 1 to75 kN/cm, in particular in the range of 2 to 70 kN/cm and refer to adiameter of 1000 mm and an average flake thickness of 10 mm. As a rule,the roll press is operated at a roll peripheral speed in the range of0.05 to 1.6 m/s. In this way, flakes are usually obtained which aresubjected to controlled crushing to adjust the particle size. The flakescan be crushed in a known manner, for example by crushing in suitableequipment, such as impact crushers, impact mills or roll crushers.

Actual granulation often follows a maturing phase. For this purpose, thefreshly prepared fertilizer granulate, which is also referred to belowas green granulate, remains at rest, i.e. stronger mechanical loads areavoided so that no further particle occurs. Here, the fertilizergranulate reaches its actual strength. Maturation typically occurs atelevated temperature, e.g. of at least 40° C., in particular at least50° C. more particularly at least 55° C. or at least 65° C., butpreferably at temperatures of not more than 80° C., in particular below80° C., to avoid conversion of the urea, e.g. to biuret. Preferably, thematuration phase is performed at temperatures in the range of 40 to 80°C. in particular in the range of 50to 80° C. more particularly in therange of 55 to 80° C. or in the range of 65 to 80° C. The duration ofthe maturation phase or the residence time of the granulate in thematuration phase is typically 5 min to 1 hr and especially 10 to 30 min.Typically, the granulate is allowed to cool down during the maturationphase. Cooling can be performed for example by an air stream. As aresult additional water, released during cooling, is removed. Typically,the process will be such that the green fertilizer granulate dischargedfrom the granulation device is transported via a so-called maturationbelt to a classifier or to a cooling apparatus. It is also possible toclassify the still warm granulate and then dry the fraction with thetargeted grain size (good fraction or good grain) in an air stream.

As a rule, classification of the fertilizer granulate follows the actualgranulation process, i.e. agglomeration and drying or compaction anddrying, if necessary. Here, separation of the granulate occurs intogranulate with the specified grain size, smaller granulate, i.e. finefraction or undersized, and possibly coarser granulate, i.e. coarsefraction or oversizes. Specifically suitable is a granulate, inparticular, in which at least 70 wt %, in particular at least 80 wt %,especially at least 90 wt % of the granulate particles have a grain sizeor a grain diameter in the range of 1 to 10 mm, in particular 2 to 8 mm.The classification can be performed by conventional methods, inparticular by sieving.

The non-specification granulate material, the so-called return material,which is generated during classification, is usually recycled back intothe process. Surprisingly, both the undersized and the oversized grainsmay be recycled to the process. The over-sized grain is usually groundup to a particle size suitable for agglomeration prior to the recycling.However, it can also be supplied to another application.

The specification-compliant granulate thus obtained can be prepared in aconventional manner, e.g. packed and transported.

A typical system for large-scale production of fertilizer granulateaccording to the invention typically comprises separate reservoirs forurea and for the magnesium sulphate hydrate, and possibly anotherreservoir for micronutrients, which are connected via a common conveyor,such as a conveyor belt with a dosing hopper. A device for preheatingthe components of the salt composition, a so-called preheater, may beprovided between the conveying device and the dosing hopper. Thecomponents of the salt composition are mixed in the conveying device andin the optional preheater. From the dosing hopper, the salt compositionis then fed into the granulation apparatus, for example an intensivemixer, such as an Eirich mixer or a compaction device or a combinationof an intensive mixer and a compaction device. The granulation apparatustypically comprises means for heating, means for cooling, e.g. forintroducing cooling air, means for temperature control and means forsupplying water in addition to means for feeding-in the salt compositionand means for discharging the granulate. The granulate discharged fromthe granulation apparatus is then typically placed on a maturation bandand transported to a classifier. In the classifier, the granulate isseparated into the good grain, i.e. granulate with the targeted grainsize, into undersized grain, i.e. granulate with a grain size smallerthan the targeted size, and into oversized grain, i.e. granulate with agrain size larger than the desired size. The undersized grain istypically returned directly to the dosing hopper. The oversized graincan be returned as such in the dosing hopper. But the oversizedgranulate may also be ground and then the ground oversized granulate canbe returned to the dosing hopper. The good grain is typically cooled inthe air stream and then optionally packed.

The fertilizer granulate obtainable by the process according to theinvention is distinguished by a sufficient strength for fertilizergranulate and, thus, by a lower sensitivity to mechanical stress, whichcould occur for example during storage or withdrawal or when handling ortransporting the granulate. This manifests itself in less graindestruction and lower dust formation through abrasion, i.e. of particleswith grain sizes below 1 mm. Therefore, granulate obtained according tothe invention tends to cake to a lesser extent during storage, inparticular under pressure, as may occur in heaps or when stored insilos. Surprisingly, the improved mechanical strength of the granulateis maintained even when stored for long periods of time, so that themechanical stresses occurring during the removal or during the handlingof the granulate obtained according to the invention lead to a lowergrain destruction even after prolonged storage.

Another advantage of the fertilizer granulate according to the inventionis that they have a low NH₃ emission, presumably because constituents ofthe granulate have a urease-inhibiting action. In other words, the ureacontained in the granulate according to the invention is less degradedthan conventional urea. Therefore, when using the granulate of theinvention in fertilizer applications, it is generally possible todispense with urease inhibitors or to reduce the quantity needed duringapplication. In principle, however, it is possible to use the granulateaccording to the invention with urease inhibitors.

One object of the invention is therefore the use of a fertilizergranulate according to the invention as fertilizers or in fertilizercompositions.

One preferred embodiment is the use as fertilizers or in fertilizercompositions which have a reduced NH₃ emission after application. NH₃emission is considered in comparison with a similar fertilizer granulatecontaining the same amount of urea. In the comparative fertilizergranulate, the urea is present preferably as conventional urea.

Reduced NH₃ emission is presumably based on the fact that the ureacontained in the granulate according to the invention is less degradedby ureases than conventional urea.

The following figures and examples serve to illustrate the invention:

FIG. 1: SEM image of a section of a representative granule from Example2.

FIG. 2: SEM image of a representative granule from Example 4.

FIG. 3: SEM image of a representative granule from Example 5.

FIG. 4: X-ray powder diffractogram of a crushed granule from Example 2.

FIG. 5: X-ray powder diffractogram of a crushed granule from Example 4.

FIG. 6: X-ray powder diffractogram of a crushed granule from Comp.Example 5.

FIG. 7: X-ray powder diffractogram of a crushed granule from Example 24.

FIG. 8: SEM image of a representative granule from Example 24.

The burst strength or breaking strength was determined with the aid ofthe tablet breaking strength tester model TBH 425D from the ERWEKAcompany on the basis of measurements on 56 individual granules ofdifferent particle size (fraction 2.5-3.15 mm), and the mean value wascalculated. The force required to break the granule between the punchand plate of the breaking strength tester was determined. Granules witha burst strength >400 N and those with a burst strength <4 N were notincluded in averaging.

Abrasion values were determined by a rolling drum process/methodaccording to Busch. For this purpose, 50 g of the granulate with aparticle size fraction of 2.5-3.15 mm were placed together with 70 steelspheres (diameter 10 mm, 283 g) in a tumble drum of a commerciallyavailable abrasion tester, e.g. ERWEKA, model TAR 20, and rotated for 10min at 40 rpm (revolutions per minute). Subsequently, the contents ofthe drum were sieved using a sieve with a mesh size of 5 mm, under whicha sieve with a mesh size of 0.5 mm was positioned, for 1 min on asieving machine (model Retsch AS 200 control). The sieved fine fractioncorresponds to the abrasion.

X-ray powder diffractometry: The respective granulate was crushed with amortar and a pestle into a powder. The ground granulate was subsequentlyexamined by X-ray powder diffractometry. The X-ray powder diffractogramwas recorded with a Bragg-Brentano process diffractometer, model D 8,from the Endeavor company, AXS (298 K, Cu-K_(α)-radiation: λ=1.5413 Å),increment: 0,018385738, increment duration: 0.2 seconds, detector: LynxEye, reflection geometry in range 2θ=8°-70°. The specified latticedistances were calculated from the determined 2θ values.

The composition of the granulate was determined by the followingmethods:

-   N-determination: association method VDLUFA II.1—Association of    German Agricultural Analytic and Research Institutes e.V. (VDLUFA),    3.5.2.7 and association method VDLUFA 11,1, 3.9.2*,-   Mg/S determination: association method VDLUFA (K+S 0905.01),-   Boron/zinc determination: DIN EN ISO 11885 (E22),-   H₂O determination by Karl Fischer titration.

The amount of water-insoluble magnesium sulfate was determinedindirectly by first determining the total magnesium content, bycompletely dissolving the crushed material in deionized water containing1 wt % of nitric acid and the determining the amount of magnesium in theaqueous solution as above. Then, a second portion of the crushedmaterial is dissolved in deionized water of pH 7 at 22° C. for 24 h withstirring. The insoluble matter is removed by filtration and the amountof magnesium in the aqueous solution is determined by elementalanalysis. The difference between the total amount of magnesium and theamount of soluble magnesium is the amount of insoluble magnesium.

The granulate was embedded in epoxy resin for sample preparation for theSEM or EDX examination. After curing of the two-component resin, thesamples were ground planar using silicon carbide. The samples were notvaporised with electrically conductive layers.

The SEM images were taken with an EVO 50EP scanning electron microscopefrom the company CARL ZEISS SMT (SE detector, VPSE G3 detector, LM4QBSD).

The EDX was performed with the “Noran System Six” microanalyser systemwith an LN₂-cooled detector with a resolution of 129 eV for MnK_(α) fromthe company Thermo. The system is integrated in the SEM.

For the preparation of the fertilizer granulate of examples 1 to 4 and 6to 9, a synthetic magnesium sulphate monohydrate (SMS-1) was used, whichwas prepared in the following manner:

Calcined magnesite (MgO-content about 80-85%) was reacted with about 70wt % aqueous sulphuric acid in a molar ratio Mg:H₂SO₄ of about 0.9. Theproduct thereby obtained, with a temperature of about 115-120° C., wastaken directly behind the mill of the reactor. The magnesium sulphategranulate thereby obtained had a total magnesium-content of at least 27wt %, calculated as MgO, and a content of water-soluble magnesium of atleast 25 wt %, calculated as MgO. The amount of water-insolublemagnesium salts was 2 wt %. The SMS thereby obtained contained less than10 wt % of particles having a particle size <2 microns and less than 10wt % of particles having a particle size of >250 microns (determined bylaser light diffraction according to ISO 13320:2009-10).

For the preparation of the fertilizer granulate of comparative example5, a mixture of two kieserite fractions was used in the mass ratio 1:1,comprising a fine (kieserite M) and a coarser (kieserite E) with thefollowing particle size distributions: kieserite M contained less than10 wt % of particles with a particle size <5 microns and less than 10 wt% of particles having a particle size of >250 microns (determined bylaser light diffraction according to ISO 13320:2009-10). Kieserite Econtained less than 10 wt % of particles with a particle size <100microns and less than 10 wt % of particles having a particle sizeof >900 microns (determined by laser light diffraction according to ISO13320:2009-10).

For the preparation of the fertilizer granulate of examples 12, 16, 20,24, 25, 27, 28, 29, 32 and 33, a synthetic magnesium sulphatemonohydrate (SMS-2) was used, which was prepared from calcined magnesiteby analogy to SMS-1. It contained less than 10 wt % of particles havinga particle size <100 microns and less than 10 wt % of particles having aparticle size of >300 microns (determined by laser light diffractionaccording to ISO 13320:2009-10). The SMS-2 contained 2 wt % of waterinsoluble magnesium, calculated as MgO, and had a total magnesiumcontent of 27 wt %, calculated as MgO.

For the preparation of the fertilizer granulate of example 36 and 37, asynthetic magnesium sulphate monohydrate (SMS-3) was used, which wasprepared from calcined magnesite by analogy to SMS-1. It contained 90 wt% of particles having a particle size of mesh 40-60 (250-420 μm,determined by laser light diffraction according to ISO 13320:2009-10).The SMS contained 2.7 wt % of water insoluble magnesium, calculated asMgO, and had a total magnesium content of 27%, calculated as MgO.

In comparative examples 9, 13, 17, 21, 26, 30, 31, 34 and 35, akieserite was used, which contained less than 10 wt % of particles witha particle size <70 microns and less than 10 wt % of particles having aparticle size of >300 microns (determined by laser light diffractionaccording to ISO 13320:2009-10).

In comparative examples 11, 14, 18 and 22, a magnesium sulphatedihydrate was used, which contained less than 10 wt % of particles witha particle size <70 microns and less than 10 wt % of particles having aparticle size of >300 microns (determined by laser light diffractionaccording to ISO 13320:2009-10).

In comparative examples 10, 15, 19 and 23, a magnesium sulphatetrihydrate was used, which contained less than 10 wt % of particles witha particle size <70 microns and less than 10 wt % of particles having aparticle size of >300 microns (determined by laser light diffractionaccording to ISO 13320:2009-10).

For urea, a commercially-available prilled urea was used with anitrogen-content of 46 wt %. The prill was ground to a powder containingless than 10 wt % of particles having a particle size <5 microns andless than 10 wt % of particles having a particle size of >300 microns(determined by laser light diffraction according to ISO 13320:2009-10).

In Examples 6 and 8, a finely divided zinc sulphate monohydrate having acontent of 35.0 wt % of zinc and a sulphur content of 17.0 wt % wasused.

In Example 8, a commercially-available borax pentahydrate was used witha boron content of 14.0 wt %.

In Example 7, the boron source used was a calcined ulexite(CaNa[B₅O₆(OH)₆].5 H₂O) with a boron content of 14.9 wt %.

The granulation described below in examples 1 to 8 (group A ofembodiments) was performed in an intensive mixer from the companyMaschinenfabrik Gustav Eirich GmbH & Co. KG (model intensive mixer R01),hereinafter known as “Eirich mixer”. The Eirich mixer had a fillingvolume of 5 L. Per preparation about 2 to 2.5 kg of salt mixture wereused.

EXAMPLE 1

52.3 parts by weight of SMS-1 were placed in an intensive mixer from theEirich company and heated to 75° C. This was followed by addition of45.2 parts by weight of urea and mixing at a speed of 600 rpm for 5minutes, initially adding 2.5 parts by weight of water incountercurrent. In this case, the mixture became increasingly liquid andhad a viscid consistency. Subsequently, the stirring speed was reducedto 100-200 rpm to promote granulate formation. From this point on, themixture was allowed to cool for a period of 10 min., and the excesswater produced by the reaction was removed via a turbulent air stream.At temperatures below 60° C., the mass hardened to form a solidgranulate.

Examples 2 to 8 were performed in an analogous manner but with amodified salt composition. The salt composition used in each case andthe amount of added water are summarised in Table 4. The compositions ofthe granulate determined according to elemental analyses are listed inTable 5. The mechanical properties of the granulate obtainable accordingto the invention are summarised in Table 6.

In all examples, the crystalline phase of formula (I) could be detectedby X-ray powder diffractometry (see also FIGS. 4 to 6).

TABLE 4 feedstock materials/input materials Magnesium sulphate UreaWater Micronutrients Example [PBW]¹⁾ [PBW] [PBW] [PBVV] 1 SMS-1 52.345.2 2.5 — — 2 SMS-1 42.2 54.8 3.0 — — 3 SMS-1 35.4 61.2 3.4 — — 4 SMS-117.3 78.5 4.2 — — 5 ²⁾ Kieserite 40.5 57.0 2.5 — — 6 SMS-1 37.0 54.3 3.0ZnSO₄ · H₂O 5.7 7 SMS-1 37.7 49.0 3.0 calc. ulexite 10.3 8 SMS-1 38.853.5 1.5 ZnSO₄ · H₂O + Na2BO7 · 5 H₂O 2.9 + 3.3 ¹⁾BW = parts by weight²⁾ Comparative Example

TABLE 5 Elemental composition of the granulate: Mg tot ¹⁾ Mg ws ²⁾ S N BZn Example [wt %] [wt %] [wt %] [wt %] [wt %] [wt %] 1 8.51 7.88 10.4020.79 0 0 2 6.88 6.37 8.40 25.20 0 0 3 5.76 5.34 7.04 28.16 0 0 4 2.812.61 3.44 36.12 0 0 5 ³⁾ 6.60 6.60 8.73 26.19 0 0 6 6.02 5.58 8.33 24.980 2.00 7 6.15 5.69 7.51 22.52 1.53 0 8 6.20 5.74 7.58 22.73 0.50 1.00 ¹⁾Mg tot: Magnesium, total ²⁾ Mg ws: Magnesium, water soluble ³⁾Comparative Example

TABLE 6 Mechanical properties of the granulate: Burst strength AbrasionExample [N] [%] 1 45 0.1 2 40 0.1 3 39 0.1 4 34 0.3 5* 20 0.2 6 42 0.1 751 0.4 8 47 0.4 *Comparative Example

A SEM examination of a granulate from Example 2 gave the followingresult—see FIG. 1. The grain had a regular shape and was a conglomerateof several particulate components embedded in a matrix of anothermaterial. A cross section is shown in FIG. 1. The particulate componentsof the grain and the matrix were analysed for elemental composition byEDX. The components appearing evenly dark in the figure (arrow 1) wereidentified as urea due to the associated elemental composition. Theparticulate components (arrow 3) appearing white coloured wereidentified as magnesium sulphate monohydrate. The matrix consistedlargely of the crystalline phase of formula (I) (arrow 2).

SEM studies of representative grains of Example 4 (FIG. 2) and Example(5) (FIG. 3) gave a result comparable to Example 2. In FIGS. 2 and 3,arrow 1 points to a region which, according to EDX analysis, consistsessentially of urea. Arrow 2 indicates a region which, according to EDXanalysis, consists essentially of the crystalline phase of formula (I)and arrow 3 indicates an area consisting essentially of magnesiumsulphate monohydrate.

FIG. 4 shows an X-ray powder diffractogram taken from crushed granulateof Example 2. The presence of the crystalline phase of formula (I), ureaand magnesium sulphate monohydrate (kieserite) was detected on the basisof the reflections characteristic of the respective phase.

FIG. 5 shows an X-ray powder diffractogram taken from crushed granulateof Example 4. The presence of the crystalline phase of formula (I), ureaand magnesium sulphate monohydrate (kieserite) was detected on the basisof the reflections characteristic of the respective phase.

FIG. 6 shows an X-ray powder diffractogram taken from crushed granulateof Comparative Example 5. The presence of the crystalline phase offormula (I), urea and magnesium sulphate monohydrate (kieserite) wasdetected on the basis of the reflections characteristic of therespective phase.

In FIGS. 4 to 6, the reflections characteristic of the respectivecrystalline phase are indicated as follows:

-   ▴ Crystalline phase of formula (I)-   ▪ Urea-   ● Magnesium sulphate monohydrate (kieserite)

FIG. 7 shows an X-ray powder diffractogram taken from crushed granulateof Example 24. The presence of the crystalline phase of formula (II),urea and magnesium sulphate monohydrate (kieserite) was detected on thebasis of the reflections characteristic of the respective phase.

In FIG. 7, the reflections characteristic of the respective crystallinephase are indicated as follows:

-   ♦ Crystalline phase of formula (II)-   ▪ Urea-   ▾ MgSO₄.H₂O (Kieserite phase)

Comparative Examples 9, 10, 11, 13, 14, 15, 17, 18, 19 and inventiveexamples 12, 16 and 20: Group A of embodiments

Examples 9 to 20 were carried out by analogy to the protocol of example1 using a intensive mixer with a rotating mixer and a rotating barrelhaving an internal volume of 50 L and a hot air heating jacket. Therotating mixer was operated with a rotation speed of 800 rpm and thebarrel with a rotating speed of 27 rpm. Urea and the respectivemagnesium sulphate hydrate were added to the barrel and heated to thetemperature T1 given in Table 7. Heated water was added to the barrel atthe beginning of the process. The mixture was mixed for mixing timet_(mix). At the end of the mixing excess water produced by the reactionwas removed via a turbulent air stream. In examples 10-20 the granuleswere held for 6-12 h at the temperature T2.

The amounts of urea and added water, the type and amount of magnesiumsulphate hydrate and the temperatures are given in the following Table7:

TABLE 7 Urea MgSO₄ Water T1 T2 t_(mix) Ex. [kg] type ¹⁾ [kg] [%] ²⁾ T [°C.] [° C.] [° C.] [min]  9³⁾ 5.0 A 5.0 4.90 60 68 -- 16.0 10³⁾ 5.0 B 5.04.00 65 71 60 23.0 11³⁾ 5.0 C 5.0 1.68 70 68 62 10.5 12 5.0 D 5.0 4.6057 74 68 14.5 13³⁾ 7.4 A 3.7 4.55 64 71 71 24.0 14³⁾ 7.4 C 3.7 1.80 6172 70 16.5 15³⁾ 7.4 B 3.7 3.20 62 70 59 15.0 16 8.0 D 4.0 4.83 60 76 7826.5 17³⁾ 8.25 A 5.5 4.00 58 72 67 17.5 18³⁾ 8.25 C 5.5 1.09 60 72 6110.0 19³⁾ 8.25 B 5.5 2.18 62 80 62 11.0 20 9.75 D 6.5 2.95 63 65 63 24.5¹⁾ A: kieserite; B: magnesium sulphate trihydrate; C: magnesium sulphatedihydrate; D: SMS-2 ²⁾ wt % of water with respect to the total amount ofurea and magnesium sulphatehydrate ³⁾comparative examples containingless than 0.1 wt % of water-insoluble magnesium salts with respect tothe total amount of magnesium, calculated was Mg.

Comparative Examples 21 to 23 and Inventive Example 24:Group B1 ofEmbodiments

The granulate was prepared according to the following protocol:

-   (1) In a heatable intensive mixer with a capacity as described for    example 9 urea and magnesium sulphate were added at ambient    temperature and intensively mixed for the mixing time given in table    8 with the desired amount of water having ambient temperature.-   (2) Subsequently, the mixture was evenly fed into a laboratory press    and compacted. A double roller press was used for this purpose,    which had two counter-rotating rollers (diameter 140 mm, length    200 mm) with trough-shaped recesses (length 6 mm×width 6 mm×depth    1.6 mm). The press was operated with a roller speed of 72 rpm. The    specific press force was individually adjusted for each test, taking    care to obtain a uniform scabbing flakes, which was crushed by means    of crusher followed by sieving to remove fines of a diameter below    2 mm. The salt mixture was fed by means of a plug screw arranged    above the press rolls. The feed rate of mixture was about 10 to 20    kg/min.-   (3) The mini briquettes obtained in step (2) were heated in a vented    oven for 6-12 h to the temperature T3 given in Table 8.-   (4) The heated briquettes were cooled to ambient temperature and    subjected to grain separation and rounding of the individual grains    .-   (5) The material obtained in step (4) was then screened. The    screening was carried out in the grain size range 4.5-5.6 mm, which    represents the product fraction. The fraction with grain size <4.5    mm can be fed back to the feed in step (2) (fine material). The    fraction with grain size >5.6 mm (coarse material) can be fed back    into the step (4).

TABLE 8 Urea MgSO₄ Water T3 t_(mix) Ex. [kg] type ¹⁾ [kg] [%] ²⁾ T [°C.] [° C.] Ex. 21³⁾ 10.0 A 5.0 2.33 25 70 16.0 22³⁾ 10.0 C 5.0 2.00 2570 23.0 23³⁾ 10.0 B 5.0 1.33 25 70 10.5 24 15.0 D 7.5 2.22 25 70 14.5 ¹⁾A: kieserite; B: magnesium sulphate trihydrate; C: magnesium sulphatedihydrate; D: SMS-2 ²⁾ wt % of water with respect to the total amount ofurea and magnesium sulphate hydrate ³⁾comparative examples

The granules obtained in examples/comparative examples 9 to 24 wereanalysed with X-ray powder diffractometry as described above. In each ofthe probes, the crystalline phase of the formula (II) was present. Theintensity of the reflections indicated that the phase of the formula(II) was present in an amount of at least 10 wt % of the granulate. Inaddition, the characteristic reflections of crystalline urea wereobserved in each of the granules, indicating that non-reacted urea waspresent. In the granulate of examples 12, 16, 20 and 24 the kieseritephase was observed. In comparative Examples 9, 10, 11, 13, 14, 15, 17,18, 19 the phase of formula (IV) was present in amounts of at least 10wt % of the granulate, while it was absent or less pronounced in thegranulates of inventive examples 12, 16 and 20.

A SEM examination of a granulate from Example 24 gave the followingresult—see FIG. 8. The grain was a conglomerate of several particulatecomponents embedded in a matrix of another material. A cross section isshown in FIG. 8. The components of the grain and the matrix wereanalysed for elemental composition by EDX. The components appearingevenly dark in the figure (arrow 1) were identified as urea due to theassociated elemental composition. The matrix consisted partly of thecrystalline phase of formula (II) (arrow 2) and also of magnesiumsulphate monohydrate (arrow 3). In addition, particles of Mg containingsilicates (arrow 4) and MgO (arrow 5) were present.

Examples 25, 27 to 29, 32, 33, 34, 36 and 37 and Comparative Examples26, 30, 31, 34 and 35: Group B1 of Embodiments

The granulate was prepared by analogy to the protocol of examples 21 to24 using a large scale granulation equipment and a rotary heater andcooler for heating and cooling the granulate exiting the double rollerpress. The relative amounts of urea, magnesium sulphate hydrate andwater, the mixing time and the heating temperature are summarized inTable 9.

TABLE 9 Urea/MgSO₄ Water T3 t_(mix) Ex. Type MgSO₄ ¹⁾ (w/w) [%] ²⁾ T [°C.] [° C.] [min] 25 D 1:1 2-3 25 60-70 5 26⁴⁾ A 1:1 2-3 25 60-70 5 27 D1:1 2 25 50 5 28 D 1:1 2 25 60 5 29 D 1:1 2 25 65 5 30³⁾ A 1:1 3 25 60 531³⁾ A 1:1 3 25 65 5 32 D 2:1 2-3 25 60-70 5 33 D 4:1 2-3 25 60-70 534³⁾ A 2:1 2-3 25 60-70 5 35³⁾ A 4:1 2-3 25 60-70 5 36 D# 1:1 2 25 60 537 D# 1:1 2 25 65 5 ¹⁾ A: kieserite; D: SMS-2 D#: SMS-3 ²⁾ wt % of waterwith respect to the total amount of urea and magnesium sulphate hydrate³⁾comparative examples

The granules obtained in examples/comparative examples 27 to 37 wereanalysed with X-ray powder diffractometry as described above. In each ofthe examples, the crystal-line phase of the formula (I) was present,except for comparative example 34. In examples 27, 32, 33, 36 and 37 andin comparative example 34 a crystalline phase of the formula (II) wasobserved. The intensity of the reflections indicated that the phases ofthe formulae (I) and (II) were present in an amount of a least 5 wt % ofthe granulate. In addition, the characteristic reflections ofcrystalline urea were observed in each of the granules, indicating thateach of theses phases were present in an amount of a least 10 wt % ofthe granulate. In comparative examples 31, 32, 34 and 35 the crystallinephases of formulae (III) and (IV) were clearly present, while they wereabsent or less pronounced in examples 27 to 29, 32, 33, 36 and 37. Inthe granulate of examples 27 to 29, 32 and 33 the kieserite phase waspresent.

TABLE 10 Elemental composition Mg tot ¹⁾ Mg ws ²⁾ N S Moisture Example[wt %] [wt %] [wt %] [wt %] [wt %] 25 9.20 n.d. 20.20 n.d. ³⁾ 0.9 26⁴⁾7.90 7.90 22.70 n.d.  0.5 29 9.35 8.39 n.d. 10.83  0.2 31⁴⁾ 8.24 8.24n.d. 11.20  0.1 32 6.34 5.32 n.d. 7.27 0.4 33 4.06 3.52 n.d. 4.33 0.234⁴⁾ 5.21 5.19 n.d. 6.87 0.1 35⁴⁾ 3.51 3.49 n.d. 4.80 0.1 ¹⁾ Mg tot:Magnesium, total ²⁾ Mg ws: Magnesium, water soluble ³⁾ n.d.: notdetermined ⁴⁾comparative examples

TABLE 11 Mechanical properties of the granulate: Burst strength AbrasionExample [N] [%]  9²⁾ 29  n.d. ¹⁾ 12 51 n.d. 13²⁾ 25 n.d. 14²⁾ 25 n.d. 1641 n.d. 17²⁾ 27 n.d. 20 43 n.d. 21²⁾ 21 n.d. 22²⁾ 16 n.d. 23²⁾ 16 n.d.24 24 n.d. 25 52 n.d. 26²⁾ 22 n.d. 27 35 n.d. 28 32 1.4 29 31 n.d. 30²⁾20 n.d. 31²⁾ 21 n.d. 32 24 0.0 33 22 0.0 34²⁾ 19 1.1 35²⁾ 13 4.0 36 291.4 37 30 1.6 ¹⁾ n.d.: not determined ²⁾not according to the invention

Test Procedure for Determining the NH₃ Emission of the Granulate

To determine the NH₃ emission of the granulate, a sample of therespective fertilizer was applied to a defined amount of soil in asealable, airtight vessel (soil with 63 soil points as representativeaverage, moisture of the soil was about 16 wt %). The lid of the vesselwas a pierced rubber stopper through which a Dräger tube for detectionof ammonia protruded into the interior of the vessel. Depending on thedegree of NH₃ emission, a colour change from yellow to blue can beobserved after some time with the Dräger tube due to the formation ofammonia as the decomposition product of the fertilizer. The height ofthe blue-coloured portion in the Dräger tube correlates with the amountof ammonia formed.

As a product according to the invention, the granulate from Example 2was tested. As a reference, a sample of pure urea and a commercialurea-based fertilizer with urease inhibitor (UI) was used, each with theexact same total amount of urea as in the experiment with the granulatefrom Example 2. Comparison of all Dräger tubes showed that the largesttotal amount of ammonia formed when using pure urea as fertilizer. Inthe granulate from Example 2, an average ammonia formation was observed.The lowest amount of ammonia was found in the commercial fertilizer withUI admixture.

1. Fertilizer granulate, which contains magnesium, sulphate and urea,each with respect to the total weight of the granulate, in the followingquantities: urea, in a quantity of 20.0 to 38.0 wt %, calculated aselemental nitrogen; magnesium in a quantity of 1.5 to 9.5 wt %,calculated as elemental magnesium; and sulphate in a quantity of 2.7 to12.0 wt %, calculated as elemental sulphur; wherein at least a portionof the magnesium, the urea and the sulphate is present in the form of atleast one of the crystalline phases of the formulae (I) and (II)MgSO₄*6 NH₂—C(═O)—NH₂.0.5 H₂O   (I)MgSO₄*4 NH₂—C(═O)—NH₂.H₂O   (II) and wherein 1 to 20 wt % of themagnesium, with respect to the total quantity of the magnesium containedin the fertilizer granulate, calculated in each case as elementalmagnesium, is present in the form of water-insoluble magnesium salts. 2.The fertilizer granulate according to claim 1, containing sulphate andurea in a ratio such that the mass ratio of nitrogen to sulphur is inthe range of 1.8:1 to 10.5:1.
 3. The fertilizer granulate according toclaim 1, wherein a portion of the magnesium in the fertilizer granulateis present in the form of magnesium sulphate monohydrate, or in the formof magnesium sulphate 5/4-hydrate or as a mixture of magnesium sulphatemonohydrate with magnesium sulphate 5/4-hydrate.
 4. The fertilizergranulate according to claim 1, wherein 3 to 18 wt % of the magnesium,with respect to the total quantity of the magnesium contained in thefertilizer granulate, calculated in each case as elemental magnesium, ispresent in the form of water-insoluble magnesium salts.
 5. Thefertilizer granulate according to claim 1, wherein at least 10 wt % ofthe urea contained in the fertilizer granulate is present in the form ofat least one of the crystalline phases of formulae (I) or (II).
 6. Thefertilizer granulate according to claim 1, wherein at least 70 wt % ofthe granule particles of the fertilizer granulate have a particle sizein the range of 2 to 10 mm.
 7. The fertilizer granulate according toclaim 1, wherein the total amount of magnesium, sulphate and urea is atleast 80 wt %, based on the total mass of the fertilizer granulate minusany water contained therein.
 8. The fertilizer granulate according toclaim 1, additionally containing a trace element from the group ofboron, manganese, zinc, copper, iodine, selenium, cobalt, iron andmolybdenum, preferably in a total amount of 0.1 to 5.0 wt %, withrespect to the total mass of the fertilizer granulate.
 9. The fertilizergranulate according to claim 1, wherein at least a portion of the ureain the granulate particles is present in the form of urea particlesembedded in a matrix of sulphate salts of magnesium.
 10. The fertilizergranulate according to claim 1, which does not contain more than 2% byweight of unbound water.
 11. A process for producing a fertilizergranulate according to claim 1, which comprises providing a salt mixturecontaining a magnesium sulphate hydrate, a water insoluble magnesiumsalt and particulate urea, wherein the weight ratio of the total weightof magnesium salts to urea is in the range of 1.2:1 to 1:5 and wherein 1to 20 wt % of the magnesium, with respect to the total quantity of themagnesium contained in the salt mixture and calculated in each case aselemental magnesium, is present in the form of water-insoluble magnesiumsalts, and subjecting the salt mixture to a granulation process in thepresence of added water.
 12. The process according to claim 11, whereinthe magnesium sulphate hydrate and the water insoluble magnesium saltare provided as a solid reaction mixture obtainable by reaction of acaustic magnesium oxide or magnesium carbonate with a sub-stoichiometricamount of sulfuric acid.
 13. The process according to claim 12, whereinthe reaction mixture contains the water-insoluble magnesium salts in anamount from 0.5 to 7 wt %, based on the total weight of the solidreaction mixture and calculated as MgO.
 14. The process according toclaim 11, wherein the salt mixture contains water-insoluble magnesiumsalts in an amount from 3 to 18 wt %, based on the total quantity of themagnesium contained in the salt mixture and calculated in each case aselemental magnesium.
 15. The process according to claim 11, wherein thesalt mixture consists of at least 80 wt %, with respect to the totalmass of the salt mixture minus any water contained therein, of magnesiumsulphate hydrate, the water insoluble magnesium salt and urea.
 16. Theprocess according to claim 11, wherein the main quantity of water isadded to the salt mixture before or at the beginning of the granulationprocess.
 17. The process according to claim 11, wherein the amount ofadded water is 1.5 to 8 wt %, with respect to the mass of urea used forgranulation.
 18. The process according to claim 11, wherein at least 80%of the particular urea has a particle size in the range from 1 to 1000μm.
 19. The process according to claim 11, which is carried out as apress granulation of the salt mixture by means of a roller press in thepresence of added water.
 20. The process of claim 19, where the pressgranulation comprises providing the salt mixture containing a magnesiumsulphate hydrate, a water insoluble magnesium salt and particulate ureaby mixing, subjecting the obtained salt mixture to a compactiongranulation to obtain granules and subsequently heating the granules.21. The process of claim 20, wherein the granules are heated to atemperature in the range from 50 to 80° C.
 22. The process according toclaim 11, which is carried out as a mixed agglomeration process using anintensive mixer, in particular an Eirich mixer.
 23. The processaccording to claim 22, wherein the agglomeration is performed at atemperature in the range of 55 to 80° C.
 24. The process according toclaim 22, wherein the agglomeration process is performed such that inthe course of agglomeration the reaction mixture temporarily takes on aviscid form.
 25. The process according to claim 22, wherein at least aportion of the water contained in the reaction mixture is removed duringagglomeration.
 26. A method for fertilizing soil, comprising applying afertilizer granulate according to claim 1 as fertilizer or in fertilizercompositions to the soil being fertilized.
 27. The method according toclaim 26, wherein the NH₃ emission of the fertilizer granulate isreduced.